1. Field of the Invention
This invention relates to vehicle wiper systems in general, and specifically to an improved park mechanism for the wiper arm of such a wiper system.
2. Description of the Related Art
Vehicle wiper systems generally include one or more blade carrying wiper arms that are swept out across the windshield from a lowermost position to an outermost position and then back in by a drive mechanism that the operator turns on and off. A common drive mechanism includes a switch controlled electric motor that rotates a crank through a motor driven output gear, in one direction. The crank in turn oscillates a link system joined to the wiper arms. Each full rotation or turn of the crank corresponds to one full cycle of the wiper arm or arms, and the wiper arms and crank are correlated so that the full extension position of the crank corresponds to the lowermost position of the the wiper arms. When the crank is located symmetrically to either side of its full extension position, the wiper arms will be at substantially the same point on the windshield, above their lowermost position. However, the wiper arms will be then moving in opposite directions, either toward or away from their lowermost position. The typical wiper system also includes a mechanism to stop the motor and crank at a suitable time after the operator turns the wiper control switch off, thereby stopping the wiper arms, or "parking," them, as it is generally known. A common park mechanism includes a circuit that continues power to the motor after the switch is turned off, regardless of where the wipers happen to be in their wipe cycle at that time, until the crank reaches a predetermined position, at which point the motor, crank and wiper arms are stopped. This predetermined stop position of the crank is generally not the full extension position of the crank, but is instead located to one side or the other of the full extension position. Consequently, the park position of the wiper arms on the windshield surface will be above the lowermost position of the wiper arms, with the wiper arms moving always in the same direction just prior to stopping, whether toward or away from the lowermost position. Consequently, when parked, the wiper blades will be flexed always in the same position. This tends to give the wiper blades a permanent set over time, which is detrimental to long blade life.